1. Field of the Invention
This invention relates to the cleaning of the interior surfaces of conduits. More particularly, it relates to the improved cleaning of conduits having difficult to remove deposits on said interior surfaces thereof.
2. Description of the Prior Art
The Sandjet process has been developed to facilitate the in-situ cleaning and drying of pipelines and the decoking and cleaning of furnace tubes. In accordance with this process, cleaning particles are entrained in a propelling fluid stream and introduced into the conduit to be cleaned at a velocity sufficient to effect the desired cleaning action. For pipeline applications, the cleaning particles generally comprise an abrasive material, such as flint, whereas in other applications, impact resistant, non-angular, non-abrasive particles, such as steel shot, are employed as cleaning agents.
The use of steel shot in the decoking of fired heater tubes is described in the Nunciato et al. patent, U.S. Pat. No. 4,297,147. As noted therein, the Sandjet process using steel shot particles provides significant advantages as compared with the known alternative decoking approaches, such as turbining, hydroblasting and steam-air decoking. ln addition to the advantages noted in the patent, there is a growing appreciation in the art of the energy savings that can be derived as a result of furnace tubes having been decoked by means of the Sandjet process as compared with the results obtainable by the most frequently used alternative approach, i.e. steam-air decoking.
While steel shot is found to have a highly effective impact cleaning action on coke deposits, certain high heat duty or thermally abused furnace applications result in the formation of difficult-to-remove coke deposits that are not removed to the extent desired by the Sandjet process using steel shot as the cleaning agent. Such deposits have likewise been found generally resistant to angular, abrasive cleaning agents, such as flint. In addition, cleaning agents such as flint are found to cause severe erosion of the bends of furnace tubes, even in cases where a difficult-to-remove deposit may not have been satisfactorily removed by such agents from the straight sections of said tubes. While non-angular particles, such as steel shot, are non-abrasive in character, it has been found that such particles will also tend to cause minimal erosion of the bends of furnace tubes treated by the Sandjet process, likewise even in cases where a difficult-to-remove deposit may not have been satisfactorily removed from the straight sections of the tubes. The problem of erosion of bends is particularly important in furnace tube sections having welded return bends, in which such erosion may lead to premature tube failure and the need for additional furnace down-time for replacement of the eroded bends. When plugged headers are employed in place of welded bends, on the other hand, bend erosion problems are of lesser consequence.
While the effectiveness of cleaning is obviously an important measure of the performance of the Sandjet process, or of any other cleaning technique, the trade-off or balance between the desirable cleaning action achieved, and the undesired erosion resulting from the cleaning operation, is often of equal or greater importance in determining the success of the operation. Thus, in some instances, an improvement in the cleaning action of the cleaning agents is desired, while the highly desirable advantages associated with the Sandjet process are retained, with the associated erosion being tolerable in particular applications. In other instances, however, improvements in the Sandjet process are desired, particularly with respect to difficult-to-remove deposits, such that an advantageous balance of desired cleaning action and undesired erosion is achieved. It will be appreciated that such an improvement in cleaning action and/or in the balance of cleaning action and erosion effect is of interest not only in the indicated furnace tube decoking applications, but with respect to other suitable applications of the Sandjet process, such as in pipeline cleaning and drying, heat exchanger tube descaling and other cleaning applications.
It is an object of the invention, therefore, to provide an improved Sandjet process for the in-situ cleaning of the interior surfaces of conduits.
It is another object of the invention to provide a process for the in-situ cleaning of conduits containing difficult-to-remove deposits.
It is another object of the invention to provide a process for the propelling of particles through a conduit to be cleaned with an enhanced cleaning action with respect to the deposits on the interior surfaces thereof.
It is a further object of the invention to provide a process for the propelling of cleaning particles through a conduit to be cleaned at an advantageous balance of desired cleaning action and undesired erosion or abrasion for a given application.
With these and other objects in mind, the invention is hereinafter described in detail, the novel features thereof being particularly pointed out in the appended claims.